Two distinct, functionally independent adhesion mechanisms in marine sponges.

In contrast to cells from other multicellular organisms, cells from the marine sponge Geodia cydonium are provided with Ca++-dependent adhesion mechanisms only (W.E.G. Müller; Intern. Rev. Cytol. 77; 1982, 129). Two different mechanisms have been discovered by us, which were termed primary aggregation and secondary aggregation. In previous reports, we described that two macromolecules (aggregation factor [sAF] and aggregation receptor [AR]) are involved in the secondary aggregation of sponge cells. The sAF was bound to a high-molecular-weight particle and was termed aggregation complex. The aggregation complex was shown to consist of two further functional subunits: UDP-glucuronosyltransferase and UDP-beta-D-galactosyltransferase. The AR with a molecular weight of approximately 17,000 was found to be a glycoprotein with D-glucuronic acid as the terminal sugar moiety. Data are presented from in vitro and in vivo experiments with the Geodia system, indicating that cell aggregation and cell separation are controlled first by alteration of the binding capacity of the aggregation receptor and secondly by an additional molecule (anti-aggregation receptor), which can decrease the interaction between the aggregation factor and the aggregation receptor. Recently we succeeded in the identification and isolation of the primary aggregation factor (pAF) from the same sponge species. This pAF is a glycoprotein that is firmly associated with the cell membrane. The Mr of the native pAF was 36,000; under denatured conditions three protein species were identified in the pAF preparation. We hypothesize that in contrast to the secondary aggregation, the initial aggregation of Geodia cells is mediated by the one-component system, the bivalent and bifunctional pAF. A new, very exciting era began with the discovery that sponges are already provided with transplantation immunopotentialities.